More than one third of the counties in the United States could face a "high" or "extreme" risk of water shortage due to climate change by 2050, according to a study published Wednesday.

The new study, carried in the Journal of Environmental Science & Technology, also concluded that 70 percent of the more than 3,100 U.S. counties could face "some" risk of shortage of fresh water for drinking, farming and other uses.

Population growth is expected to increase the demand for water for municipal use and for electricity generation beyond existing levels, Sujoy Roy, a researcher from California-based Terra Tech Research and Development, and colleagues said in the analysis.

Global climate change threatens to reduce water supplies due to decreased rainfall and other factors compared with levels in the 20th century, they said.

Roy's group developed a "water supply sustainability risk index" that takes into account water withdrawal, projected growth, susceptibility to drought, projected climate change and other factors in individual U.S. counties for the year 2050.

It takes into account renewable water supply through precipitation using the most recent downscaled climate change projections and estimates future withdrawals for various human uses.

The team used the index to conclude that climate change could foster an "extreme" risk of water shortage that may develop in 412 counties in southern and southwestern parts of the United States.

"This is not intended as a prediction that water shortage will occur, but rather where they are more likely to occur, and where there might be greater pressure on public officials and water users to better characterize, and creatively manage demand and supply," Roy said.